Don't output "Warning" twice
Don't output "Warning" twice

Currently, I get output like this:

WARNING: Unknown section 'dpi' in 'xxx.core'
WARNING: Warning: Unknown item "top_module" in section "xsim" in yyy.core

This commit removes the second "Warning".

lowRISC/fusesoc,lowRISC/fusesoc,olofk/fusesoc,olofk/fusesoc